Hindawi Publishing Corporation
International Journal of Chemical Engineering
Volume 2012, Article ID 329419, 9 pages
doi:10.1155/2012/329419
Research Article
Gas-Solid Reaction Properties of Fluorine Compounds and Solid
Adsorbents for Off-Gas Treatment from Semiconductor Facility
Shinji Yasui,1 Tadashi Shojo,2 Goichi Inoue,2 Kunihiko Koike,2
Akihiro Takeuchi,3 and Yoshio Iwasa3
1 Nagoya
Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555, Japan
Corporation, 4-5-1 Katsube, Moriyama-shi, Shiga 524-0041, Japan
3 Chubu Electric Power Co., Inc., 20-1 Kitasekiyama, Odaka-cho, Midori-ku, Nagoya 459-8522, Japan
2 Iwatani
Correspondence should be addressed to Shinji Yasui, [email protected]
Received 23 March 2012; Accepted 19 June 2012
Academic Editor: Annabelle Couvert
Copyright © 2012 Shinji Yasui et al. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
We have been developing a new dry-type off-gas treatment system for recycling fluorine from perfluoro compounds present in
off-gases from the semiconductor industry. The feature of this system is to adsorb the fluorine compounds in the exhaust gases
from the decomposition furnace by using two types of solid adsorbents: the calcium carbonate in the upper layer adsorbs HF
and converts it to CaF2 , and the sodium bicarbonate in the lower layer adsorbs HF and SiF4 and converts them to Na2 SiF6 . This
paper describes the fluorine compound adsorption properties of both the solid adsorbents—calcium carbonate and the sodium
compound—for the optimal design of the fixation furnace. An analysis of the gas-solid reaction rate was performed from the
experimental results of the breakthrough curve by using a fixed-bed reaction model, and the reaction rate constants and adsorption
capacity were obtained for achieving an optimal process design.
1. Introduction
Fluorocarbons and perfluoro compounds (PFCs) contribute
to global warming and are used in large quantities in the
semiconductor industry, which must reduce the emission
of these gases to the atmosphere in order to achieve the
requirements of the Kyoto Protocol. In the semiconductor
industry, voluntary reduction goals for PFCs were set at
the World Semiconductor Council held in April 1999 and
ongoing reduction efforts have been made. However, since
hydrofluorocarbons (HFCs) and PFCs are used in critical
processes, including chamber cleaning and etching during
the manufacturing of semiconductors such as LCDs and solar
panels, the consumption of these chemicals increases every
year. Therefore, in spite of the reduction efforts, the emission
of fluorocarbons and PFCs has increased in recent years.
The technology for the treatment of PFCs, which has
been supplied in the semiconductor industries as an inexpensive process, is a combination of combustion to decompose
PFCs into acid components such as HF and scrubbing to
neutralize the acid components [1]. However, because the
combustion method has a low decomposition ratio and the
treatment of the resultant wastewater has a high energy load,
a new dry treatment technology is desirable. Consequently,
we are developing a new dry-type treatment technology for
PFCs that consists of an electric furnace for decomposition
of the PFCs and a dry-fixation furnace for adsorption of the
acid components, which enables fluorine recycling. Fluorine
is a precious resource for Japan, which imports most of its
fluorine from China or Mexico [2]. This paper describes
the details of the treatment process, the gas-solid reaction
properties of fluorine compounds, and solid adsorbents in
the dry-fixation furnace of the fluorine recycling system.
2. Dry-Type Treatment System
The processing flow of the treatment system being developed
is shown in Figure 1. The treatment system is divided into
three parts. In the semiconductor industry, silane (SiH4 )
is used for Si deposition, and NF3 is mainly used as the
chamber-cleaning gas. These gases are used alternately in the
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N2
NF3
SiF4
SiH4
H2 O
N2 , HF, SiF 4
Dry-fixation
furnace
CaCO3
for HF recovery
Electric furnace
for NF3 decomposition
HF
SiF4
SiO2
NaHCO3
for SiF4 recovery
Teflon filter
for SiO2 recovery
N2 , H 2 O, CO 2
Switching the
flow channel
Figure 1: Schematic of the dry-type gas treatment system.
chamber; that is, the exhaust gases from the process chamber
include SiH4 , NF3 , and SiF4 diluted with N2 through the
vacuum pump. Initially in the treatment process, NF3 and
SiH4 are decomposed in the electric furnace to form HF,
SiF4 , and SiOx . The SiOx powder is then removed using a
Teflon filter, and the remaining HF and SiF4 are adsorbed by
solid adsorbents in the subsequent dry-fixation furnace. The
dry-fixation furnace is a switching system with two columns,
each filled with an upper layer of calcium carbonate and a
lower layer of sodium bicarbonate; the calcium carbonate in
the upper layer adsorbs HF and converts it to CaF2 and the
sodium bicarbonate in the lower layer adsorbs HF and SiF4 to
convert them to Na2 SiF6 . These chemical reactions are shown
as follows:
2HF + CaCO3 −→ CaF2 + H2 O + CO2
(1)
HF + NaHCO3 −→ NaF + H2 O + CO2
(2)
SiF4 + 2HF + 2NaHCO3 −→Na2 SiF6 + 2H2 O
+ 2CO2
(3)
The vapor and CO2 byproducts do not require further
treatment. Because the Teflon filters have to be processed at
low temperatures, less than 200◦ C, it is desirable to process
the gas-solid reaction of each adsorbent at a low temperature
of 150◦ C for negligible reheating system. The treatment flow
rate in the developing system is 300 L/min (3% NF3 and 0.5%
SiH4 in N2 ) from emissions from the three chambers of the
semiconductor-processing device.
The purpose of the dry-fixation furnace in this system
is to generate high-purity calcium fluoride during the offgas treatment. The reaction properties of each adsorbent are
shown in Figure 2. The role of the sodium bicarbonate is
to adsorb any HF gas breakthrough from the CaCO3 layer
by converting it to high-purity calcium fluoride and also to
adsorb SiF4 gas during the treatment process, because SiF4
gas does not react with CaCO3 at a low temperature of 150◦ C.
3. Fixed-Bed Reaction Model
In order to achieve the optimal design of the reaction vessel
of the dry-fixation furnace, we investigated the reaction
property of HF gas and the solid adsorbent of CaCO3 . We
used the fixed-bed reaction model for analyzing this reaction
property. By assuming that the distribution of the HF gas
concentration as the gas moved from inlet to outlet in the
CaCO3 layer remained constant, the reaction rate of HF and
CaCO3 in the fixed-bed furnace can be estimated from the
differential time of the HF concentration in the outlet gas
breakthrough from the fixed-bed furnace.
Under the isothermal conditions in the fixed-bed furnace
and by negligible volume change of the reactive gases, the
mass balance of the HF component at the cross-sectional area
in the fixed-bed furnace is given by the following equation
using the symbols defined in Figure 3:
v
∂η
∂C
∂CHF
+ ε HF = − .
∂x
∂t
∂t
(4)
The reaction zone of the HF gas and CaCO3 is formed in
the fixed-bed furnace, as shown in Figure 4, and the zone is
moved forward to the outlet at the constant velocity of uS .
Under these conditions, the HF gas flowing into the furnace
accumulates in the solid adsorbent, and the reaction zone is
moved only by the amount of the accumulation. The mass
balance at this time is represented by the following equation:
0
= uS · η0 .
v · CHF
(5)
In the steady state, the time change of the molar concentration of HF in the fixed-bed furnace is determined by
the moving velocity of the HF concentration curve with
a constant shape, and the relationship between them is
represented by the following equation:
∂CHF
∂CHF
= −uS
.
∂t
∂x
(6)
The following equation is obtained from (4), (5), and (6):
ε−
η0 ∂CHF
∂η
=− .
0
∂t
∂t
CHF
(7)
The following relationship is satisfied in our fixed-bed
furnace:
ε
η0
.
CHF
(8)
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3
Reaction ratio of adsorbent
NaHCO3 layer
CaCO3 layer
1
HF
0
CaCO3 layer
NaHCO3 layer
HF
SiF4
Inlet
Recovery of high-purity of
CaF2
Outlet
NaF
Inlet
(a) Reaction property of CaCo3
Outlet
Na2 SiF6
(b) Reaction property of NaHCO3
Figure 2: Schematic of the dry-type gas treatment system.
dx
L
x
0
CHF /CHF
t2
uS
0
: Inlet HF molar concentration (mol/cm3 )
CHF
L: Fixed-bed length (cm)
ε, η, CHF
1
1
v: Space velocity (cm/min)
CHF : HF molar concentration (mol/cm3 )
t1
tB
x: Position from inlet of fixed-bed (cm)
ε: Void ratio of fixed-bed (—)
η: HF reaction molar quantity per unit volume
of fixed-bed (mol/cm3 )
η0 : HF saturation reaction molar quantity per
unit volume of fixed-bed (mol/cm3 )
0.5
0
0
Outlet
0
x
tB t1 t2
tE
L
Figure 5: Breakthrough curve as compared with inside phenomenon on fixed-bed reactor.
0
v, CHF
Figure 3: Description of material balance of fixed-bed reaction
furnace.
By evaluating this relationship at the outlet part of the fixedbed furnace, this equation can be expressed as ordinary
differential equations:
0
d CHF /CHF
0
CHF
dt
0
Inlet
Reaction zone
x
d η/η0
=
.
dt
Outlet
Figure 4: Inside phenomenon on the fixed-bed furnace.
ηg
η
= 0,
η0
ηg
From (7) and (8), the relationship between HF molar
adsorption quantity per unit volume of fixed-bed furnace
and the HF molar concentration can be expressed by the
following equation:
0
∂ CHF /CHF
∂t
∂ η/η0
=
.
∂t
(10)
Therefore, HF molar adsorption quantity per unit volume at the outlet of the fixed-bed furnace and the HF
gas concentration in the gas exhausted from the fixed-bed
furnace obtained by the experiments show the same changes
for the reaction time, as shown in Figure 5. The ratio η/η0 is
the normalized fluoride ratio of CaCO3 . The fluoride ratio
does not change even if the saturation amount is changed
from the per unit volume to the per unit weight, so the
following equation is obtained:
uS
tS
where ηg is the HF molar adsorption quantity per unit weight
and ηg0 is the HF adsorption capacity per unit weight of
CaCO3 . Finally, the following relationship can be obtained
from (10) and (11):
(9)
(11)
d η/η0
dt
=
d ηg /ηg0
dt
.
(12)
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Table 1: Experimental conditions for the gas-solid reaction.
Practical system Experimental conditions
Processing flow rate
400 L/min
1.6 L/min
Inner diameter
45 cm
2.8 cm
Superficial velocity
6 cm/s
6 cm/s
L/D ratio
1.2
1.2
120 kg
31 g
CaCO3 weight
6700 h−1
Space velocity (SV)
400 h−1
Adsorbent size
1∼2 mm, 2∼5 mm
1∼2 mm, 2∼5 mm
150◦ C
Fixation temperature
150◦ C
the off-gas from the fixed-bed reactor increased gradually
after the moment of breakthrough and finally reached the
initial concentration at the entrance of the fixed-bed reactor.
The results shown in the vertical axis in Figure 7 were
normalized by the initial HF concentration at the entrance.
The elapsed time from the breakthrough point to the
0
= 1) increased under
complete breakthrough time (CHF /CHF
low HF concentration conditions. For a fixed-bed reactor,
0
)/dt)
the differential of the breakthrough curve (d(CHF /CHF
can be regarded as equal to the reaction rate (dX/dt) of the
CaCO3 filling the outside edge of the fixed-bed reactor:
X=
In this research, the reaction rate of HF gas and the solid
adsorbent CaCO3 was evaluated by the differential value
of the breakthrough curve of HF concentration in the
exhaust gases obtained by the fundamental experiments.
This fixed-bed reaction model was used in the analysis of the
desulfurization catalyst quality [3, 4].
4. HF Breakthrough Properties of CaCO3
In our previous studies, the reaction rates of HF gas and the
solid adsorbent CaCO3 were investigated in the fundamental
experiments for the purpose of the recovering fluoride from
the waste fluorocarbons [5, 6]. In these studies, the reaction
conditions of HF gas concentration were very high, 35%–
60%. In a semiconductor factory, the concentration of the
cleaning gas NF3 in the off-gas is less than about 5% at
most, so the HF concentration in the exhaust gases from the
electric decomposition furnace is assumed to be less than
about 10%. Therefore, the reaction rate of HF and CaCO3
was investigated in the low HF concentration conditions.
4.1. Experimental Conditions and Method. The important
parameters for the design of reactors for gas-solid reactions
are the particle size of the solid adsorbents, reaction temperature, and superficial velocity. The experimental conditions
are consistent with the design specifications of these parameters for a practical system. The design specification and the
experimental parameters are shown in Table 1.
The experiment flow is shown in Figure 6. The reaction
gas, including HF gas, was obtained by thermal decomposition of HFC134a (C2 H2 F4 ) with water vapor and diluted
at the entrance of the fixed-bed reaction furnace. The fixedbed reactor filled with calcium carbonate is made of stainless
steel, which is heated uniformly in a vertical electric furnace.
The temperature of the vertical electric furnace was set at
150◦ C. HF gas concentrations of 1%, 5%, and 10% and
CaCO3 grain sizes of 1-2 mm and 2–5 mm were investigated.
The breakthrough properties for each experimental condition were investigated by measuring the concentration of
F ions in the impinger. The concentration of F ions was
measured by using a F− ion sensor and ion chromatograph.
The experimental conditions are summarized in Table 2.
4.2. Experimental Results. The results of the breakthrough
properties are shown in Figure 7. The HF concentration in
CHF
0 ,
CHF
(13)
where X is the reaction ratio of CaCO3 . Therefore, the slopes
of the breakthrough curves of these results were evaluated
and plotted against the HF concentration at the slope points,
as shown in Figure 8. From these results, the reaction rate
of CaCO3 can be determined using a first-order reaction
formula of the HF concentration.
The results of the reaction rates of CaCO3 were investigated using the gas-solid reaction model of a shrinking
unreacted core system. The reaction rate of a shrinking
unreacted core system is expressed using the following
equation [7]:
CHF
dX
=
.
dt
fS−1 · (1 − X)−2/3 + f p −1 · (1 − X)−1/3 − 1 + fg −1
(14)
Here, fS is the rate constant for the particle surface chemical
reaction, f p is the rate constant for diffusion through the
product layer of a spherical particle, and fg is the rate
constant for the external mass transport. By evaluating the
results of Figure 8 using (14), the overall reaction rate of
CaCO3 could be expressed in terms of the two rate constants:
the rate constant for diffusion through the product layer ( f p )
and the rate constant for external mass transport ( fg ) as
shown in Figure 9.
Evaluating the slope and the intercept of the straight lines
in Figure 9, each rate constant was obtained as shown in
Table 3.
By using each obtained rate constant, it was possible
to calculate the elapsed time from the initial breakthrough
point to the complete breakthrough point by setting the
0
) and the reaction ratio of
initial concentration of HF (CHF
CaCO3 (e.g., 0.95). From this calculated time, the amount
of HF gas leaking from the CaCO3 layer until the CaCO3
was converted into high-purity CaF2 was calculated from the
treatment flow rate. This indicates the amount of HF gas that
needs to be adsorbed in the subsequent NaHCO3 layer.
5. SiF4 Adsorption Properties of
Sodium-Based Adsorbents
The purpose of the NaHCO3 layer is to adsorb the HF
and SiF4 exhausted from the CaCO3 layer. To determine
the amount of NaHCO3 needed, it is necessary to calculate
1
2
3
4
5
6
Test
no.
Ar
H2 O
Air
N2
Total
5
20
40
5
20
40
300
300
300
300
300
300
50
75
150
50
75
150
100
150
300
100
150
300
1100
1000
700
1100
1000
700
1555
1595
1590
1555
1595
1590
20
80
160
20
80
160
0.574
2.239
4.492
0.574
2.239
4.492
[mol/m3 ]
HF flow rate HF concentration
Pyrolysis gas conditions
[mL/min] [mL/min] [mL/min] [mL/min] [mL/min] [mL/min] [mL/min]
C2 H2 F4
Flow rate of the treated gases
Type Weight Grain size
[g]
[mm]
1∼2
CaCO3 31
CaCO3 31
1∼2
CaCO3 31
1∼2
CaCO3 31
2∼5
CaCO3 31
2∼5
CaCO3 31
2∼5
Adsorbent
Table 2: Experimental conditions of the gas-solid reaction of HF and CaCO3 .
150
150
150
150
150
150
[ C]
◦
Reaction temperature
Fixation conditions
6.1
6.2
6.2
6.1
6.2
6.2
4408.4
4295.5
4394.3
4408.4
4295.5
4394.3
Space
SV
velocity
[cm/s] [h−1 ]
1.2
1.2
1.2
1.2
1.2
1.2
L/D
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6
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Dry type
fixation furnace
Mass flow controller
Mass flow controller
N2
F− ion sensor
Ar
HFC
Out
Tubular furnace
(∼1,273 K)
Water
manometer
Humidifier
(partial pressure ∼0.7)
Air
HF absorption
by impinger
Active carbon
and silica gel
Temperature trace tube
1
0.8
0.8
0.6
0.4
0.2
0.6
0.4
0
100
600
800
1000
t (min)
(a) HF conc.: 1%
0.8
0.6
0.4
0.2
0.2
0
150
200
250
t (min)
(b) HF conc.: 5%
(A) Grain size: 1-2 mm
40
300
1
1
0.8
0.8
0.8
0.6
0.4
0.2
0
CHF /CHF
(—)
1
0
CHF /CHF
(—)
0
CHF /CHF
(—)
0
400
1
0
CHF /CHF
(—)
1
0
CHF /CHF
(—)
0
CHF /CHF
(—)
Figure 6: Experiment flow of the gas-solid reaction of HF and CaCO3 .
0.6
0.4
0.2
0
0
400
800
t (min)
(a) HF conc.: 1%
1200
0
60
80 100 120 140
t (min)
(c) HF conc.: 10%
0.6
0.4
0.2
0
60
120 180 240 300
t (min)
(b) HF conc.: 5%
(B) Grain size: 2–5 mm
0
20
60
100
140
t (min)
(c) HF conc.: 10%
180
Figure 7: HF breakthrough properties of CaCO3 .
the adsorption capacity of each gas. By the fundamental
experiments in our studies, the amount of NaHCO3 needed
for HF adsorption was confirmed to supply an equimolar
amount of HF leaked from the CaCO3 layer because the
reaction of NaHCO3 and HF at 150◦ C generate not only
NaF and NaHF2 but also HF can be completely adsorbed by
an equimolar amount of NaHCO3 . Therefore, this section
describes the results of the experiments for examination of
the adsorption capacity of SiF4 .
5.1. Experimental Conditions and Method. The experimental
flow is shown in Figure 10. At first, HF was generated by
thermal decomposition of HFC134a (C2 H2 F4 ) with water
vapor and air; SiF4 was generated by the reaction of the
HF and pieces of quartz. Then, these reaction gases were
introduced into the fixed-bed furnace with N2 dilution gas
to establish the SiF4 concentration and then reacted with
sodium-based adsorbents in the furnace. We used two types
of sodium-based adsorbents: NaHCO3 and NaF. NaF was
International Journal of Chemical Engineering
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0.02
0.03
X = 0.5
0.02
X = 0.3
0.015
X = 0.5
X = 0.7
X = 0.7
0.015
dX/dt (min−1 )
dX/dt (min−1 )
0.025
X = 0.9
X = 0.1
0.01
X = 0.3
X = 0.9
0.01
X = 0.1
0.005
0.005
0
0
0
1
2
3
CHF (mol/m3N )
4
0
5
(a) Grain size: 1-2 mm
1
2
3
CHF (mol/m3N )
4
5
(b) Grain size: 2–5 mm
Figure 8: Reaction rate of CaCO3 plotted against the HF concentration.
350
(dX/dt)−1 ·CHF ((mol min)/m 3N )
(dX/dt)−1 ·CHF ((mol min)/m 3N )
350
300
250
200
X = 0.9
150
X = 0.7
100
X = 0.5
50
X = 0.3
0
X = 0.1
0
0.2
0.4
0.6
0.8
1
(1 − X)−1/3 −1 (—)
1.2
300
250
200
X = 0.9
150
X = 0.7
100
X = 0.5
X = 0.3
50
0
1.4
X = 0.1
0
0.2
0.4
0.6
0.8
1
1.2
1.4
(1 − X)−1/3 −1 (—)
(a) Grain size: 1-2 mm
(b) Grain size: 2–5 mm
Figure 9: Plots of (dX/dt)−1 · CHF versus (1−X)−1/3 −1.
Table 3: Rate constants of the gas-solid reaction of HF and CaCO3 .
f p = 6.67 × 10−3 [m3 /(mol·min)]
f p = 5.37 × 10−3 [m3 /(mol·min)]
Grain size 1-2 mm
Grain size 2–5 mm
fg = 1.88 × 10−2 [m3 /(mol·min)]
fg = 1.17 × 10−2 [m3 /(mol·min)]
Dry type
fixation furnace Mass flow controller
Mass flow controller
N2
Tubular furnace
SiF4 generation
(∼1,273 K)
C2 H2 F4 Air
Humidifier
(partial pressure ∼0.7)
FTIR
Active carbon
HF
absorption and silica gel
Temperature trace tube
Figure 10: Experimental flow of the gas-solid reaction of SiF4 and sodium adsorbents.
International Journal of Chemical Engineering
100
100
80
80
Concn. (ppm)
Concn. (ppm)
8
60
40
60
40
20
20
0
0
0
50
100
150 200
t (min)
250
300
350
0
HF
SiF4
50
100
150 200
t (min)
250
300
HF
SiF4
(a) NHCO3
(b) NaF
Figure 11: Breakthrough properties of HF and SiF4 .
1 mm
Component
F content
(a) Before reaction
(b) During reaction
(c) After reaction
Figure 12: EPMA photographs of the CaCO3 adsorbents before and after experiments.
1 mm
During
reaction
After
reaction
(a) Component
(b) F content
(c) Si content
Figure 13: EPMA photographs of the NaHCO3 adsorbents before and after experiments.
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Table 4: Experimental conditions of the fixed-bed furnace.
W
g
NaHCO3 or NaF 12
T
C
150
◦
V
cm3
10.4
L
cm
1.68
L/D
—
0.60
v
cm/s
11.7
SV
h−1
25066
used because it is generated by the reaction of HF and
NaHCO3 in the fixed-bed furnace. The concentrations of
HF and SiF4 in the exhaust gas from the fixed-bed furnace
were analyzed by Fourier-transform infrared spectroscopy
(FT-IR), and the amount of SiF4 adsorbed by each adsorbent
up to the moment of breakthrough was determined. Table 4
shows the gas-solid reaction conditions of these experiments.
5.2. Experimental Results. Figure 11 shows the results of
the breakthrough properties of each adsorbent. The breakthrough times of SiF4 in both adsorbents were more than
200 min from after the start of the gas-solid reaction.
Because the concentration of SiF4 was less than 3 ppm,
which is the TLV value of SiF4 , until the breakthrough time,
it was confirmed that both sodium-based adsorbents can
completely adsorb SiF4 . The breakthrough times for the
NaHCO3 and NaF adsorbents were 230 min and 250 min,
respectively. The adsorption capacity of each adsorbent was
then calculated using that obtained time to be 0.133 g-SiF4 /gNaHCO3 and 0.145 g-SiF4 /g-NaF. NaHCO3 can adsorb both
the HF and SiF4 that leak from CaCO3 layer. The amount
of NaHCO3 filling the fix-bed furnace can be calculated
using the obtained adsorption capacities for each gas by the
amount of CaCO3 loading in the fixation furnace.
6. Chemical Analysis of the Obtained Fluorides
The major advantage of this dry-treatment system is the
ability to recycle the obtained fluorides. This section shows
the chemical properties of the obtained fluorides. Figure 12
shows the EPMA photographs of the cross-section of the
calcium adsorbents before and after the reactions. It is
confirmed that the reaction with fluorine proceeds to the
core of the calcium adsorbent. Mg and Si impurities are
detected at about several hundred or several thousand ppm
in the obtained calcium fluorides. These impurities are
originally contained in the raw calcium carbonate materials
as dolomite (CaMg(CO3 )2 ) and silica. However, the purity of
the obtained CaF2 is over 97%, which is sufficient for it to be
recycled as fluorine resources.
The EPMA photographs of the cross-section of the
NaHCO3 adsorbents before and after the experiments are
shown in Figure 13. Similar to the CaCO3 adsorbent, the
fluorine and silicon reaction proceeded to the core of
the adsorbents. Silicon was detected as Na2 SiF6 by X-ray
diffraction analysis. This sodium-based material can be also
reused as a special material by the fluorine industry.
7. Conclusions
In order to develop a new dry-type gas treatment system
for semiconductor facilities, the gas-solid reaction properties
of HF, SiF4 gas, and solid adsorbents in a fixation furnace
were investigated. From the experimental results of the
HF breakthrough properties of the CaCO3 adsorbent, the
apparent gas-solid reaction rate constants were obtained
by using the rate formula of the unreacted core model.
In addition, the HF and SiF4 breakthrough properties
of sodium base adsorbents of NaHCO3 and NaF were
investigated, and the adsorption capacities of each adsorbent
were obtained. From the experimental results of the gassolid reaction rate constants and the adsorption capacities,
the optimum dry-type fixation furnace can be designed.
Furthermore, by examining the chemical compositions of the
obtained fluorides, it was confirmed that the calcium fluoride
could be recycled as a fluorine resource.
Acknowledgments
This work was supported by a Grant-in-Aid for Scientific
Research (C), the Iwatani Naoji Foundation’s Research
Grant.
References
[1] Ministry of Economy, Trade and Industry, “About the Future
State of the Cure Against Discharge Control of Chlorofluorocarbon,” Ministry of Economy, Trade and Industry Report,
2006.
[2] Mineral commodity summarizes, 2010, http://minerals.usgs.
gov/minerals/pubs/mcs/.
[3] H. Shirai, M. Kobayashi, and M. Nunokawa, “Modeling of
desulfurization reaction for fixed bed system using honeycomb
type iron oxide sorbent and desulfurization characteristics in
coal gas,” Kagaku Kogaku Ronbunshu, vol. 27, no. 6, pp. 771–
778, 2001.
[4] C. B. Shumaker and R. Schuhmann Jr., “Reaction rates for
sulfur fixation with iron at 1100 to 1275 K,” Metallurgical
Transactions B, vol. 14, no. 2, pp. 291–300, 1983.
[5] S. Yasui, K. Ikeda, and H. Shirai, “Research on dry-processing
technology for reconverted resources fluorine from waste
chlorofluorocarbons,” in Proceedings of the AIChE Annual
Meeting, Salt Lake City, Utah, USA, November 2007, Paper
no.173d.
[6] S. Yasui, S. Nakai, A. Ueno, T. Utsumi, T. Imai, and T.
Murakami:, “Low temperature dry processing technology for
exhaust gases containing fluorine using calcium absorbents,” in
Proceedings of the 18th International Congress of Chemical and
Process Engineering (CHISA ’08), Prague, Czech Republic, 2008.
[7] J. Szekely, J. W. Evans, and H. Y. Sohn, Gas-Solid Reaction,
Academic Press, New York, NY, USA, 1976.
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